Cystatin C

A high cystatin C level usually indicates reduced kidney filtration (lower GFR), suggesting acute or chronic kidney dysfunction. It’s a sensitive marker less affected by muscle mass. Non-renal factors—age, inflammation, thyroid disease, steroids, smoking, obesity—can also raise levels. Elevated cystatin C prompts further evaluation, monitoring and tests by a clinician, as it’s linked to renal impairment and higher cardiovascular risk.

Cystatin C is a small protein made by all nucleated cells, freely filtered by glomeruli and reabsorbed then catabolized in tubules; its blood level reflects GFR and is less affected by muscle mass, age, sex, or diet. Creatinine is a muscle-derived metabolite whose serum level depends on muscle mass, diet and tubular secretion, making it less sensitive and more variable for early kidney dysfunction.

Cystatin C is a low‑molecular‑weight cysteine protease inhibitor produced by all nucleated cells. It regulates protease activity to protect tissues, modulate extracellular matrix remodeling, and influence inflammation. Because it is produced at a steady rate, freely filtered by glomeruli and reabsorbed and catabolized in proximal tubules, blood cystatin C level is a sensitive marker of kidney glomerular filtration rate.

Normal adult serum cystatin C is roughly 0.6–1.2 mg/L (some labs use 0.5–1.0 mg/L). Children and older adults may have different reference ranges. Higher-than-normal cystatin C suggests reduced kidney filtration (GFR). Because assay methods and cutoffs vary by laboratory, always compare your result to the lab’s stated reference interval and discuss abnormal values with your clinician.

Elevated cystatin C occurs with reduced kidney function and in several cancers, particularly hematologic malignancies such as lymphoma, leukemia and multiple myeloma, and solid tumours including lung, colorectal, gastric, pancreatic, ovarian and bladder cancers. Levels may reflect tumor burden, inflammation or cancer‑related renal impairment; interpret results alongside GFR, clinical context and other laboratory findings.

High cystatin C indicates reduced kidney function. Treatment focuses on addressing the underlying cause and slowing progression: control blood pressure and blood sugar, stop nephrotoxic drugs, adjust medication doses, reduce proteinuria (ACE inhibitors/ARBs if appropriate), optimize hydration and diet, stop smoking, and manage cardiovascular risk. Repeat testing, monitor eGFR, and refer to a nephrologist for further evaluation and possible specialist treatments.